Transcript VLBA imaging of the Gamma-ray Emission Regions in

VLBA Imaging of the γ-ray Emission
Regions in Blazar Jets
or: A Sequence of Images is Worth 1000 Light Curves
Alan Marscher
Boston University
Research Web Page: www.bu.edu/blazars
Main Collaborators in the Study
Svetlana Jorstad, Iván Agudo, & M. Joshi (Boston University)
Valeri Larionov (St. Petersburg State U., Russia)
Margo & Hugh Aller (U. Michigan) Paul Smith (Steward Obs.)
Anne Lähteenmäki (Metsähovi Radio Obs.)
Mark Gurwell (CfA)
Ann Wehrle (SSI) Paul Smith (Steward)
Thomas Krichbaum (MPIfR) + many others
Telescopes: VLBA, GMVA, EVLA, Fermi, RXTE, Swift, Herschel,
IRAM, UMRAO, Lowell Obs., Crimean Astrophys. Obs., St.
Petersburg U., Pulkovo Obs., Abastumani Obs., Calar Alto
Obs., Steward Obs., + many others
Funded by NASA & NSF
Diagram of a Quasar
Gamma-ray emission might occur inside BLR, in 7 mm core, or elsewhere along the jet
via scattering of different sources of seed photons by relativistic electrons in the jet
Method for Locating High-frequency Emission
• mm-wave VLBI imaging to follow changes in jet, especially
motions of superluminal knots
• Associate optical, X-ray, or -ray flares with superluminal
knot if flare is coincident with passage of knot through 43
GHz “core” (which is parsecs downstream of black hole)
• Measure optical polarization position angle  during flare &
match with VLBI feature with similar value of 
• Determine location of X-ray & gamma-ray emission sites by
time lag of high-E variations relative to changes in optical &
mm-wave flux or when knot is in core
Quasar PKS 1510-089 (z=0.361) in 2009
Multiwaveband monitoring: General (but not
one-to-one) correspondence between -ray
& optical
37 GHz flux starts rising at same time as
start of -ray/optical outburst
VLBA images at 43 GHz
Color: linearly polarized intenisty Contours: total intensity
Time when
knot passes
through
core
2009.0
2009.6
Bright superluminal knot passed “core” at
time of extreme optical/-ray flare
Apparent speed = 21c
Marscher et al. (2010, Astrophysical Journal Letters,
710, L126)
Rotation of Optical Polarization in PKS 1510-089
Rotation starts when major optical activity
begins, ends when major optical activity
ends & centroid of superluminal blob
passes through core
- After rotation, optical pol. angle ~ same as
that of superluminal knot
-
Also, later polarization rotation similar to
end of earlier rotation, as expected if
caused by geometry of B; event occurs
as a weaker blob approaches core
Model curve: blob following a spiral path
in an accelerating flow
 increases from 8 to 24,  from 15 to 38
Blob moves 0.3 pc/day as it nears core
Core lies > 17 pc from central engine
2009.0
2009.6
Sites of -ray Flares in PKS 1510-089
Interpretation:
All flares in early 2009 caused by a single superluminal knot
moving down jet
Sharp flares occur as knot passes regions of high photon density
or standing shocks that compress the flow or energize high-E
electrons
Standing shock system, “core”
Broad-line clouds
Knot
Sites of high optical/IR emission
in relatively slow sheath of jet
3C 279 in 2008-09
1. Multi-flare
outburst in -ray,
optical, & X-ray
after new
superluminal knot
appears
Flux
2. X-ray dominant
flare, peak after
new knot appears
3. Simultaneous ray, optical, & Xray flare near time
when superluminal
knot appears
knot
3C 454.3: Outbursts seen first at mm wavelengths
3C 454.3: 2010 super-outburst
Knot ejected in
late 2009,
vapp = 10c
RJD=5502, 1 Nov 2010; core: 10.3 Jy
RJD=5507, 6 Nov 2010; core: 14.1 Jy
RJD=5513, 12 Nov 2010; core: 14.2 Jy
RJD=5535, 4 Dec 2010; core: 17.7 Jy
OJ287 (Agudo et al. 2011, ApJL, 726, L13)
Change in jet direction
starting ~ 2005
Core is the more
southern compact
feature, C0
High-E flare near start of
mm-wave flux outburst &
~ coincident with max. in
polarization of feature C1,
which moves very slowly
Flare B appear to occur
as superluminal knot
passes through C1
Implications
• Many gamma-ray flares in blazars occur in superluminal knots
that move down the jet & are seen in VLBA images
⇒ Sometimes upstream of 43 GHz core
⇒ Often in or downstream of 43 GHz core
• Intra-day γ-ray/optical variability can occur in mm-wave regions
⇒ The highest-Γ jets are very narrow, < 1°, so at 10 pc from the
central engine, jet < 6 lt-months across
⇒ Doppler factors can be very high, >50 (Jorstad et al. 2005)
⇒ Volume filling factor of γ-ray/optical emission << 1 if very highenergy electrons are difficult to accelerate (as in turbulent jet
model of Marscher & Jorstad 2010)
• Rotations of polarization & timing of flares agree with
magnetic-launching models of jets, where jet flow accelerates
over long distances
Advantage of Wider Bandwidth/Higher Recording Rate
Currently:
 High dynamic range (> 100:1) at 43
GHz if core flux > ~0.5 Jy
 Low sensitivity/dynamic range at 86
GHz
 Cannot image knots in key TeV
blazars such as Mkn 421 with high
enough fidelity to measure motion
Mkn 421
1 Aug 2010
With upgrade (this year!):
24 Oct 2010
Bandwidth for routine observations ~ 4
times broader
 High sensitivity  higher dynamic
range
4 Dec 2010
EXTRA SLIDES FOLLOW
Movie of the Quasar 3C 273 (z=0.158) [Director: S. Jorstad]
Emission feature following spiral path down jet - rotationn
Emission feature following
spiral path down jet
of EVPA
Feature covers much of jet cross-section, but not all
Centroid is off-center
 Net B rotates as feature moves down jet, P perpendicular to B
1
3
Bnet
P vector
2
4